Because of their unique properties, epoxy resins are increasingly finding a great variety of uses in the building industry (cf. for example, H. Saechtling, "Bauen mit Kunststoffen" [Building with Synthetic Resins], Carl-Hanser Publishers, Munich, 1973). Besides the pure epoxy resin mortars, utilized, for example, for coatings and adhesive bonds, interesting possibilities of application in the building industry are also offered by epoxy resin-cement mortars due to their good adhesive srtrength, satisfactory shrinkage characteristics, and their water retention capacity.
An essential prerequisite for the use of epoxy resins is that the resin and the curing agent react, under the weathering conditions prevailing at the building site, extensively completely with each other within an adequate period of time.
The binder mixture described in DOS No. 2,840,874, consisting of an hydraulic binder, an epoxy resin, the adduct from a polyamine and an epoxy compound, water, and optionally reactive diluents, pigments, and other auxiliary agents, is particularly suitable for renovating damaged reinforced concrete parts, since the use of a corrosion-protective primer is not needed with this mixture.
A disadvantage of this bicomponent sysem is that, due to its limited stability, it must be prepared at the building site and processed within a relatively brief time span (about one-half hour). It is also known that the ratio of curing agent to epoxy resin is of decisive importance. The cited process, wherein a rapid and very careful intermixing is important lest impairment of quality occur, therefore has significant drawbacks under practical conditions.
According to U.S. Pat. No. 3,926,886, it is more advantageous to start with an epoxy resin-diammonium acetate or formate emulsion consisting of a liquid epoxy resin, water, and a substituted diammonium salt, and to effect curing in the presence of cement.
The diammonium salt has a dual function in this process. On the one hand, it is to liberate the basic diamine after reacting with the alkaline-acting cement, the diamine then curing the epoxy resin. On the other hand, it is to function as an emulsifier. However, stability of the thus-produced emulsion is not ensured, especially if the process must be carried out under extreme weather conditions. For this reason, even U.S. Pat. No. 3,926,886 suggests the addition to the mixture of up to 15% of a commercially available emulsifier. Yet, even after making such additions, the stability of the emulsion remains a disadvantageous, critical factor.
It is further unsatisfactory that only certain diamines containing ether groups and of the formula EQU R.sub.1 --O--R.sub.2 --NH--R.sub.3 --NH.sub.2
are suitable as the amine component. R.sub.1 is an alkyl of at least 8 carbon atoms and R.sub.2 and R.sub.3 are lower alkylene of 2-4 carbon atoms. In contrast, it would be desirable to use more readily available diamines for preparing emulsions. The predominant number of such diamines, however, are miscible with water in any desired ratio--in contrast to the diamines in U.S. Pat. No. 3,926,886. The formates and acetates of such other diamines cannot be emulsified with the customary emulsifiers, such as, for example, fatty alcohol oxethylates, alkyl sulfonates, or phosphoric acid half esters (monoesters). On the other hand, only homogeneous, stable emulsions are capable of ensuring, in uniform quality, cold curing of the liquid epoxy compounds utilized.